Islamic State militants released a video Tuesday saying they would kill the two men, Goto and Haruna Yukawa, unless Japan paid the money within 72 hours, linking the threat to what they said was Japan's support for efforts to fight the group.

Goto's mother said Friday her son was a friend of Islam whose life had been devoted to helping children in war zones.

"I would like to tell everyone in the Islam State that Kenji is not an enemy of the Islamic State,” said Ishido.

Foreign Minister Fumio Kishida said Friday Japan is making every effort to secure the hostages' release, but will not give in to terrorism.

"Our policy remains that we will not yield to terrorism and will work together with the related nations in the fight against terrorism," said Kishida.

Yoshihide Suga, Japan's Chief Cabinet Secretary, said Japan is doing all it can to secure the release of the men.

"We are doing our utmost to coordinate with the related nations as well as the religious and tribal chiefs," said Suga.

Japanese Prime Minister Shinzo Abe said earlier this week his country is in a "race against time" to free the two men.

The prime minister said Japan would not submit to terrorists and has pledged $200 million in non-military aid to those countries affected by the extremists.

Japan is not among the countries directly participating in the coalition battling insurgents in Syria and Iraq. However, Japanese citizens have previously been killed by Islamic militants; the most notable attack was at an Algerian gas plant in 2013 where 10 Japanese died.